Researchers suggest that guidelines endorsed by the CDC and WHO for the safe disposal of liquid waste from patients with Ebola virus disease may not be adequate to prevent water treatment workers from being exposed to the virus, according to data recently published in Water Environment Research.
Although Ebola is primarily transmitted through direct contact of bodily fluids of infected patients, Charles N. Haas, PhD, LD Betz Professor in Drexel’s College of Engineering and head of the department of civil, architectural and environmental engineering at Drexel University, and colleagues noted that there is a potential risk for sewer workers downstream of hospitals and treatment facilities to contract Ebola through inhalation.
“During the 2014 to 2016 Ebola outbreak, we had our first case of Ebola treated in the U.S., and by the end, 11 individuals had been treated here — so this is certainly an area of risk assessment that we need to examine more closely,” Haas said in a press release. “One thing we do know from previous research is that it is possible to inhale the virus to cause a risk — and it wouldn’t take much. At this point we haven’t seen a confirmed case of somebody contracting Ebola in this way, and our hope is that this work can contribute to revised guidelines that will keep it that way.”
In August 2014, WHO released guidance that recommended liquid waste from Ebola patients be discharged in the sanitary sewer without disinfection, according to the researchers. The organization issued more conservative guidelines in December 2014; however, there was no explicit recommendation for pretreating the waste before disposal. The CDC subsequently issued similar guidance, stating that “sewage handling processes in the United States are designed to inactivate infectious agents,” Haas and colleagues wrote. Nevertheless, some experts have argued that all human waste from patients with a viral hemorrhagic fever, including those infected with Ebola, should be disinfected before it is disposed into a municipal sewer system.
To better understand the potential risks for Ebola exposure in wastewater treatment facilities, the researchers spoke with sewer workers to clarify where and when they might encounter untreated aerosols. The researchers then examined data from previous studies on Ebola to develop a model of its behavior under similar circumstances. Their assessment took into consideration the amount of waste accumulated during a treatment period, the length of time between disposal and when sewer workers would be exposed to the waste, and the concentration of infectious particles in the air at the treatment facilities.
The researchers reported that the risk for exposure varied by the time spent in a contaminated area and whether workers were compliant with the CDC–recommended use of personal protective equipment (PPE).
“While an acceptable risk of [Ebola virus disease (EVD)] has not yet been defined, under the least favorable conditions in which PPE is not worn and [Ebola virus] RNA copies are deemed as virulent as [plaque-forming units], the median potential risk for developing EVD illness from inhalation exposure to EBOV–contaminated aerosols in the sewer is approximately 10-5.77, a higher value than many risk managers may be willing to accept,” they wrote. “Thus, current WHO and CDC guidance for EBOV liquid waste disposal — to dispose in the sanitary sewer without further treatment — may be insufficiently protective of sewer worker safety.” – by Stephanie Viguers
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